1. Field of the Invention
The present invention relates to a semiconductor non-volatile memory and, more particularly, to a circuit configuration for a memory cell read operation.
2. Description of the Background Art
There are increasing demands for smaller sizes and larger capacities of semiconductor non-volatile memories. For high-speed applications, VGA (Virtual Ground Architecture)-type semiconductor non-volatile memories, being one type of NOR-type memories, have often been used in view of the degree of integration. A VGA-type memory includes an uninterrupted arrangement of memory cells between all bit lines, wherein adjacent memory cells share a bit line therebetween, thereby allowing for miniaturization substantially in conformity with the 4F2 scaling law.
However, in a VGA-type memory, where every bit line is shared by adjacent memory cells, bit lines adjacent to a memory cell [characteristics are successively charged by the drain voltage application to the memory cell being read (and, albeit slightly, by the source voltage of the memory cell being read). Therefore, an excessive charge on each bit line during a previous read operation needs to be collected by a somewhat complicated process. Therefore, they are not so often used in applications where high-speed read operations are needed, and are limited to low-speed, large-capacity applications.
In recent memory systems, there are more demands for increasing the memory capacity than for the rate of miniaturization, and there is also an increasing demand for a higher read speed. Therefore, there is a strong demand for semiconductor non-volatile memories that can realize both an increase in the capacity and an increase in the speed.
Patent Documents 1, 2 and 3, identified below, propose the employment of the ground-sensing method with VGA-type semiconductor non-volatile memories.
Patent Document 1: U.S. Pat. No. 6,128,226 (FIG. 1 on page 1)
Patent Document 2: U.S. Pat. No. 6,134,156 (FIG. 6 on page 6)
Patent Document 3: U.S. Pat. No. 6,937,523 (FIG. 3 on page 2)